Card games are popular in a field of on-line games. In some card games, a user receives an allotted game item selected in response to an acquisition request from the user and the user can use the game item to progress the game.
Selection of the game item to be allotted is performed, for example, based on an allotment probability set for each game item as disclosed in Japanese Patent Application Publication No. 2008-93165 (the “'165 Publication”).
Japanese Patent No. 5335969 (the “969 patent”) discloses a game system in which a deck of a finite number of game items is allocated to a user, and an allotted game item is selected from among the game items included in the deck allocated to the user in response to an acquisition request for a game item from the user.
The allocation of a deck to each user disclosed in the '969 patent is actually adopted in many card games. In such card games, decks allocated to users are often configured to include a small number of rare items in the deck of each user. Advantageous parameters (for instance, high attack ability) are set in the rare items so users can progress games with advantages by using the rare items. It should be understood that users try to obtain rare items from own decks by using points and virtual currencies which the users have. In such card games, after all the rare items are selected from a deck, a user may often feel there are no more game items which the user wish to obtain in the deck so the deck may be initialized or a new deck is allocated to the user.
Initialized decks and decks newly allocated to users are in initial states. A deck in the initial state includes a small number of rare items and a large number of game items other than the rare items. A probability to win the rare items from the initialized deck is low and users know that they have to consume many points to obtain the rare items. Thus, users to whom the initialized deck is allocated may feel that it is a lot of work to acquire the rare items. The above-described mechanism in which an initialized deck is newly allocated to a user after the user obtains rare items from his/her deck may reduce the user's willingness to obtain rare items after the user obtained desired game items from the deck.
Moreover, there would be no strategy for efficiently obtaining desired game items such as rare items in the above-described conventional selection method of game items. In order to acquire rare items, users only had to increase the number of acquisition requests for game items. Therefore users may tend to get bored with the games because there is no strategy for obtaining rare items.